Laminated circuit boards are used widely in sensitive electronic equipment such as computers and communications equipment. Circuit boards, generally, are multi-layer composites of thermosetting polymers and suitable reinforcing materials. One suitable reinforcing material is woven glass fabric.
Such reinforcing fabrics are extremely fine, light weight and very fragile. During processing, the fabric is particularly susceptible to the presence of any residue or particulate matter that, if conductive, may cause performance malfunctions (such as short circuits) in the finished printed circuit boards. Due to such sensitivity, high standards of cleanliness and quality are imposed. Fabrics commonly are rejected if the fabrics are contaminated with any foreign particles, whether conductive or not.
Heretofore, such fabrics have been dried using hot air, contact heat, or infrared radiation. Such drying techniques are acceptable for ordinary applications in which deposits of some foreign particulate matter will not adversely affect the product or may be washed out after subsequent operations. However, these techniques have proved to be a problem where the fabric is used in the manufacture of printed circuit boards. Hot air, contact heat, and/or infrared radiation techniques are prone to leave fine particles that may contaminate the woven glass fabric. Hot air introduces a foreign fluid stream that is riddled with particulate matter. Contact heat can cause migration from one face of the fabric to another and results in uneven and non-uniform drying. Infrared radiation cannot be controlled sufficiently; therefore a mechanical shutter system must be used to prevent excessive heating of the fabric. The shutter system introduces rust, dirt, and other particulate matter to the fabric environment. Further, fiberglass fabrics are fragile and are often damaged during these harsh drying processes.
There exists a need for a more uniform and controlled drying process that achieves the necessary cleanliness and sensitivity required for fabrics to be used in laminates for electronics.